You do understand that it's actually
very difficult to get a screenwriting agent?
There are tens of thousands of amateur screenwriters trying to break into the industry, meanwhile work for the existing working pool of pro screenwriters keeps getting smaller and smaller... New material is becoming increasingly difficult to sell because the studios are favoring work with an already captured fanbase in the millions (Hunger Games, The Host, sequels, comics, non-fiction work etc). Many have left feature film work and gone to writing teleplays.
So agents are very very selective.
Have you won some well respected screenwriting contest/s?
Have some of your scripts sold?
Is your script really a killer script with a fantastic hook and concept, great characters and great dialogue? And that's based on the opinion of an industry pro, not just yourself or people (not in the industry) close to you? We can't be objective on our own work and if you're an amateur, you need the opinion of a seasoned pro - not friends and fellow amateurs.
Many agents are not interested in representing writers with just a single script (unless it is exceptional). Many want the writer to have penned at least three good scripts that they can offer to the market.
Most amateur screenwriters think their first script is outstanding (I know I did). I have written five now and been a semi-finalist in the Nicholl (Academy Nicholl Fellowships in Screenwriting), and a Finalist with 3x scripts at CWA... When I read my first script now, I cringe - it really was not very good at all.
Sorry I can't offer lots of positive guidance but the reality in today's Hollywood is that earning a career screenwriting is getting tougher and tougher.
Anyway, there is a forum dedicated to screenwriting... They have lots of agent-related questions and info.
http://messageboard.donedealpro.com/boards/
If you want impartial feedback on your script do a google on 'script coverage'. Dozens of companies offer it - some good, many terrible. Just don't pay some script 'guru' >$200 (some jokers charge $500+). I can recommend these folks [disclaimer: I have done some freelance work for them in the past] but you have many options out there.
http://reelauthors.com/